High density information recording medium and slider having rare earth metals

ABSTRACT

An information recording medium comprising an information recording film formed on a base on which regular depressions and projections having Ra of 0.1 to 1.5 nm have been formed, the information recording film containing as a major component a rare earth-transition metal amorphous alloy capable of magnetically reproducing a recorded information.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to Japanese application No. HEI11(1999)-265640 filed on Sep. 20, 1999 whose priority is claimed under35 USC § 119, the disclosure of which is incorporated by reference inits entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an information recording medium and aninformation recording and reproducing slider and, more particularly, toan information recording medium which is improved inrecording/reproducing characteristics according to which information ismagnetically recorded and reproduced, as well as to an informationrecording and reproducing slider suited to recording and reproduction ofinformation on and from the information recording medium.

2. Description of Related Art

Optical recording media such as DVDs and magnetic recording media suchas HDDs have been known and have gained popularity as informationrecording media. In addition since it has been desired to enhance therecording density of information, research has been made intomagneto-optical (MO) recording media in which the merits of opticalrecording media and the merits of magnetic recording media are combined.

According to an information recording/reproducing method of magneticallydetecting information recorded on a magnetic material of the magneticrecording medium or the magneto-optical recording medium among theabove-described recording media, as the result of more advancedresearch, it has become possible to record information at ultrahighdensity. It has presently been proved that there is a possibility ofultrahigh-density recording exceeding 10 Gbits/(inch)².

A polycrystalline magnetic material, such as Co₇₇Cr₁₅Pt6Ta₂, which hasan easy axis of magnetization in an in-plane direction is normally usedas such a magnetic material.

Use of a perpendicular magnetization film made of a rareearth-transition metal amorphous alloy as the magnetic material of themagnetic recording medium is described in Japanese Unexamined PatentPublication No. SHO58(1983)-165306. This rare earth-transition metalamorphous alloy is used as a magnetic material for magneto-opticalrecording media, and magneto-optical recording media having a laminatedbody of rare earth-transition metal amorphous alloys having differentmagnetic characteristics have recently been described in JapaneseUnexamined Patent Publication Nos. HEI5(1993)-217226, HEI5(1993)-325283,SHO63(1988)-302448 and the like.

Among them, Japanese Unexamined Patent Publication No.SHO63(1988)-302448 describes a magneto-optical recording medium having alaminated body in which a so-called rare earth (RE) rich film

More specifically, a description is made of a magneto-optical recordingmedium in which a TbFeCo film having a larger Kerr rotation angle isused as the TM rich film and a TbFeCo film capable of providing a largesignal level ({square root over (R)}•θ: R=reflectance, θ=Kerr rotatingangle) is sued as the RE rich film, and both films are exchange-coupledto each other. It is stated that this medium has advantages in that alarge SNR can be obtained because a rise in noise level can berestrained, and writing energy can be made small. In other words, it canbe considered that if the medium described in this publication is usedas a medium such as a MO disk, recording noise can be reduced whileretaining a large magneto-optical effect.

To improve the recording density to a further extent, noise which occursin an information recording medium needs to be reduced to a furtherextent. To this end, the grain size of magnetic grains (crystal grains)must be made approximately 10 nm.

However, if the grain size of the crystal grains of the above-describedpolycrystalline magnetic material is made approximately 10 nm, theresulting magnetic domains (recorded bits) become thermally unstable at,in particular, the interfaces of the crystal grains. This fact causesproblems that noise is produced in the information recording medium,recorded information disappears and the like. In particular, theadoption of such minute magnetic grains causes the problem that thecoercive force of the information recording medium becomes lower with atemperature rise (normally, the temperature inside a drive in usebecomes approximately 65° C.).

In addition, it cannot be said that the medium described in theabove-cited Japanese Unexamined Patent Publication No.SHO63(1988)-302448 is appropriate for a method of reproducing magneticflux. For example, in Example 1 of this publication, a description ismade of a medium formed of a laminated body of a magnetic film of Hc=2kOe (thickness=20 nm) and a magnetic film of Hc=10 kOe (thickness=60nm). This medium has the coercive force substantially larger than thatrecordable by a normal magnetic head, and thus the recording isdifficult.

In addition, it is in general necessary that the magnetization of amedium be large to an extent detectable by a magnetic head.

In the case of the medium of the above-cited publication, it is inferredthat the magnetization of the magnetic film of Hc=2 kOe is comparativelylarge and the magnetization of the magnetic film of Hc=10 kOe iscomparatively small. Total magnetization is the sum of the values ofmagnetization of magnetic films which constitute a medium. However, inthe case of the medium of the above-cited publication, since the filmhaving a larger magnetization is thin, its total magnetization is verysmall and the medium does not emit magnetic flux to the outside, so thatdetection by a magnetic head is difficult.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a firstinformation recording medium comprising an information recording filmformed on a base on which regular depressions and projections having Raof 0.1 to 1.5 nm or period of 10-40 nm have been formed, the informationrecording film containing as a major component a rare earth-transitionmetal amorphous alloy capable of magnetically reproducing a recordedinformation.

In addition, according to the present invention, there is provided asecond information recording medium comprising an information recordingfilm made of an exchange-coupled multilayer film capable of magneticallyreproducing a recorded information, wherein the exchange-coupledmultilayer film has a coercive force which is not substantially changedat a temperature ranging from room temperature to approximately 65° C.,the product of 55 Gauss μm or more of a remnant magnetic flux densityand a film thickness, and includes at least a transition metal-rich rareearth-transition metal amorphous alloy layer and a rare earth-rich rareearth-transition metal amorphous layer.

Furthermore, according to the present invention, there is provided aslider for recording and reproducing information used for recording orreproducing on or from above information recording medium, the slidercomprising a light irradiating means, a recording head and a magneticreproducing head that are integrated, the light irradiating means beinglocated ahead of the recording head and the magnetic reproducing head inthe direction of information recording and reproducing.

These and other objects of the present application will become morereadily apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating an informationrecording medium according to the present invention;

FIG. 2 is a schematic view illustrating a structure of a recording andreproducing apparatus;

FIG. 3 is a plan view illustrating how information is recorded and/orreproduced;

FIG. 4 is a schematic view illustrating a structure of a slider forrecording and reproducing information according to the presentinvention;

FIG. 5 is a schematic enlargement view illustrating a major part of theslider according to the present invention;

FIG. 6 is a schematic enlargement view illustrating a major part of theslider according to the present invention;

FIG. 7 is a graph illustrating a change in magnetization in accordancewith the amount of Tb contained in TbFe; and

FIG. 8 is a schematic sectional view illustrating an informationrecording medium according to Example 13 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first information recording medium according to the present inventionwill be described below.

In order to realize ultrahigh-density recording by a method which allowsa magnetic recording and reproducing method, the inventor of the presentinvention has made an examination of the use of, as an informationrecording film, a rare earth-transition metal amorphous alloy which hasgreat magnetic anisotropy and does not have crystal grains. It is knownthat this amorphous alloy has a strong exchange coupling force in theinterior of the film. For this reason and since a recording heademploying a thin-film. coil, which has been used in existing recordingand reproducing apparatuses, has large head dimensions and hence hasdifficulty in generating a sufficient magnetic field, it has beenconsidered that it is difficult to form very small recording marks bysuch a recording head. In addition, since the amorphous alloy has theproperty that the coercive force becomes smaller when the exchangecoupling force is made smaller, it has been considered that stability ofthe recording marks deteriorates. For this reason, it has not beengeneral to use the amorphous alloy for the information recording medium.

However, the inventor has made a detailed investigation into recordingcharacteristics of an information recording medium in which the rareearth-transition metal amorphous alloy was used as the informationrecording film, the structure of the information recording film and thelike, and found out unexpectedly that if appropriate depressions andprojections are formed on a base below the information recording film,an appropriate column structure is formed in the interior of themagnetic film as shown in FIG. 1. In FIG. 1, reference numerals 1, 2 and3 denote the base, a underlying layer and the information recordingfilm, respectively. Moreover, the inventor has found out that theinformation recording film having this column structure enables verysmall recording marks to be formed even with a prior art magnetic headand can also provide a large reproduced signal. Thus, the inventor hasattained the present invention.

The information recording medium of the present invention includes atleast a base and an information recording film located over the base.

Any base known to those skilled in the art can be used as long asregular depressions and projections having a predetermined Ra or periodare formed on the base. Concretely, the base may be a substrate made ofglass, ceramics, titanium, silicon, carbon or the like on which regulardepressions and projections are formed, a base on which an underlyinglayer having regular depressions and projections is formed, or the like.Incidentally, in the case where the underlying layer is to be formed, aresin substrate such as a polycarbonate substrate may be used as thesubstrate.

The method of forming the regular depressions and projections on thesubstrate may be a so-called mechanochemical polishing method in whichthe substrate is dipped in an acid such as hydrochloric acid andpolished by using a polishing agent of predetermined particle size (forexample, Al₂O₃, SiC or SiO).

The regular depressions and projections of the underlying layer may beformed at the same time as the formation of the underlying layer, or maybe formed in a separate step after the underlying layer has been formed.In the case where the regular depressions and projections are to beformed at the same time as the formation of the underlying layer, it isnecessary to select a material which enables the regular depressions andprojections on the layer to be spontaneously formed into a predeterminedshape as lamination of the layers proceeds, for example, by a sputteringmethod. Such a material may be an alloy such as NiP, NiB or CrMo, or ametal such as Cr or Ti. In the case where the regular depressions andprojections are to be formed in a step separate from the formation ofthe underlying layer, the material of the underlying layer is notparticularly limited. A method of forming the regular depressions andprojections on the underlying layer may be, for example, themechanochemical polishing method. To reduce the manufacturing processes,it is preferable to form the regular depressions and projections and theunderlying layer at the same time.

Incidentally, a NiP film formed by sputtering method has the advantagein that its particle size is small.

In the case where NiP is used for the underlying layer, the compositionof NiP is not particularly limited. For example, representativecompositions are Ni:P=4:1, 3:1, 2:1 and 5:4. However, if a film which isexcessively rich in Ni is used as the underlying layer, there occurs theproblem that Ni is precipitated and the underlying layer becomes aferromagnetic material. If the underlying layer becomes theferromagnetic material, an magnetostatic interaction between theunderlying layer and the information recording film might possibly occurand exert an influence on a recording/reproducing magnetic field. Forthis reason, the composition of NiP is preferably Ni:P=4-2:1. Normally,the composition of CrMo is Cr:Mo=approximately 90:10.

The specific shape of the regular depressions and projections is 0.1-1.5nm in Ra or 10-40 nm in period.

It is not preferable that Ra is smaller than 0.1 nm, because the columnstructure is not easily formed in the information recording film. It isnot preferable that Ra is larger than 1.5 nm, because the size of onecolumn becomes large and noise easily occurs. A more preferable Ra is0.2-1.2 nm. As the thickness of the underlying layer is made larger, Racan be made larger, whereas as the thickness of the underlying layer ismade smaller, Ra can be made smaller.

Incidentally, in the present specification, Ra is a value obtained inconformity to JIS (Japanese Industrial Standards) Surface Roughness (B0601). Specifically, a portion of measurement length L is extracted froma roughness curve in the direction toward the center line thereof, andrepresenting the center line of this extracted portion by the X-axis,the direction of axial magnification by the Y-axis, and the roughnesscurve by y=f(x). Ra means a value obtained by representing a valueobtained from the following equation by nm.${Ra} = {\frac{1}{l}{\int_{0}^{l}{{{f(x)}}\quad {x}}}}$

In addition, it is not preferable that the period is smaller than 10 nm,because the column structure is not easily formed. It is not preferablethat the period is larger than 40 nm, because the column structurebecomes larger. A more preferable period is 15-25 nm. In the case wherethe underlying layer is to be formed by sputtering method, the periodcan be controlled by adjustment of applied power, and if the appliedpower is made higher, the period becomes longer, whereas if the appliedpower is made lower, the period becomes shorter.

Incidentally, the thickness of the underlying layer is preferably 7-75nm. It is not preferable that the thickness of the underlying layer issmaller than 7 nm, because the column structure is not easily formed. Itis not preferable that the thickness of the underlying layer is largerthan 75 nm, because the grain size of a column becomes excessivelylarge.

The information recording film which includes as its major constituentthe rare earth-transition metal amorphous alloy which enables recordedinformation to be magnetically reproduced is formed over the base havingthe above-described regular depressions and projections.

Rare earth-transition metal amorphous alloys usable in the presentinvention are, for example, TbFe, TbFeCr, TbFeCo, DyFeCo, GdCo, GdFe,TbCo, GdTbFe, GdTbFeCo and GdDyFeCo. The composition of these alloys isappropriately set so that the desired coercive force and saturationmagnetization can be obtained. Among these alloys, TbCo, TbFe, TbFeCr,TbFeCo and DyFeCo are preferable.

The thickness of the information recording film is preferably 20-25 nm.

Furthermore, the information recording film of the present invention maybe made of two or more layers utilizing the magnetic exchange couplingtherebetween. For example, in the case where the information recordingfilm is made of two layers, a magnetization inversion assisting layermay be provided below the information recording film made of any of theabove-described rare earth-transition metal amorphous alloys. Themagnetization inversion assisting layer can stabilize the recordingmarks. Moreover, the information recording film may have a recordinglayer and a reproducing layer so that the recording of information andthe reproduction of information are separately performed. By thisseparation, the compositions of the respective films can be set so thattheir coercive force and saturation magnetization are suited torecording and reproduction.

The magnetization inversion assisting layer may be a perpendicularmagnetization film or an in-plane magnetization film. In addition to theabove-described amorphous alloys, a crystalline alloy such as CoCrTa canbe used for the perpendicular magnetization film. Alloys such as GdFeCoand GdFe can be used for the in-plane magnetization film. The thicknessof the magnetization inversion assisting layer is preferably 2-10 nm.

The above-described amorphous alloys can be used for the recording layerand the reproducing layer. Specific combinations are TbFe/TbFeCo,TbFe/DyFeCo, TbCo/TbFeCo and the like. The thicknesses of the recordinglayer and the reproducing layer are preferably 20-40 nm and 5-20 nm,respectively.

The method of forming the information recording film is not particularlylimited, and any known method can be used. Among known methods, asputtering method is preferably used to form the information recordingfilm.

The information recording medium of the present invention may furtherhave layers which constitute a normal information recording medium, suchas a substrate protecting layer (for example, SiN or SiO), a surfaceprotecting layer (for example, SiN or SiO) and a carbon layer forimproving the sliding characteristics of a slider. In general, thesubstrate protecting layer is located between the substrate and theinformation recording film (if the underlying layer is present, betweenthe underlying layer and the information recording film), the surfaceprotecting layer is located on the information recording film, and thecarbon layer is located a top of the information recording medium.

According to the information recording medium of the present invention,as compared with the case where no depressions and projections areformed on the base, it is possible to improve the SNR by 100% or moreand the overwrite characteristic by 400% or more. This is considered tobe due to the fact that very small recording marks can be stably formedowing to the column structure in the interior of the informationrecording film, which stems from the regular depressions and projectionsof the base.

The information recording medium of the present invention can be used asa magnetic recording medium, and also as a magneto-optical recordingmedium.

If the information recording medium of the present invention is used asthe magneto-optical recording medium, it is possible to recordinformation with a micro recording mark having a track width of, forexample, 0.1-2.5 μm and a width of magnetization inverting portion of0.1-2 μm. this information can also be reproduced with a known magneticreproducing head.

A second information recording medium of the present invention will bedescribed below.

The coercive force of an in-plane magnetization film made of CoCrTaPt,which is generally used in an information recording medium, is 3 kOe atroom temperature, but decreases to approximately 2.4 kOe at about 65° C.The coercive force of a perpendicular magnetization film made of CoCrPt,is 3 kOe at room temperature, but decreases to approximately 2.4 kOe atabout 65° C. For this reason, it has been difficult to stably use thesemagnetization films at a temperature ranging from room temperature toabout 65° C.

The inventor of the present invention has made an examination as towhether or not an information recording medium whose coercive force doesnot change with respect to temperature can be obtained with a rareearth-transition metal amorphous alloy film.

It is known that a rare earth-transition metal amorphous alloy whichincludes a rare earth element such as Tb or Dy has a particularly largeperpendicular magnetic anisotropy.

Specifically, in the case of an alloy film of TbFe, if the compositionof Tb is in the neighborhood of about 23%, as shown in FIG. 7, thereexists a so-called compensation composition in which the value ofsaturation magnetization is zero. In the present specification, a regionin which the content of Tb is larger than this compensation composition(i.e., a region in which the content of transition metal is smaller) isreferred to as a rare earth (RE)-rich region, and a region in which thecontent of Tb is smaller than the compensation composition (i.e., aregion in which the content of transition metal is larger) is referredto as a transition metal (TM)-rich region. In. FIG. 7, symbol a denotesthe range of perpendicular magnetic anisotropy, and symbol b denotes therange of in-plane magnetic anisotropy.

Although FIG. 7 shows only the value of saturation magnetization, in acomposition which has the smallest value of saturation magnetization,the coercive force reaches infinity, and as the saturation magnetizationdeviates from that value, the coercive force decreases. This phenomenonsimilarly occurs not only with respect to the composition, but also withrespect to the temperature. In other words, on the basis of the findingthat a transition metal-rich rare earth-transition metal amorphous alloylayer exhibits a decrease in coercive force and a small increase insaturation magnetization value with a rise in temperature, whereas arare earth-rich rare earth-transition metal amorphous alloy layerexhibits an increase in coercive force and a decrease in saturationmagnetization value with a rise in temperature, the inventor of thepresent invention has exchange-coupled the alloy layers to form anexchange-coupled multilyered film in which saturation magnetization isdetermined to a predetermined value. Thus, the inventor has achieved thesecond information recording medium capable of keeping the coerciveforce and the saturation magnetization nearly constant and of stablerecording and reproducing information.

The rare earth-transition metal amorphous alloy layer is made of, forexample, TbFe, TbFeCr, TbFeCo, DyFeCo, GdCo, GdFe, TbCo, GdTbFe,GdTbFeCo or GdDyFeCo. It is preferable that the alloy layer contains atleast Tb or Dy. Among these alloys, TbCo, TbFe, TbFeCr, TbFeCo andDyFeCo are particularly preferable.

The composition and materials of the transition metal-rich rareearth-transition metal amorphous alloy layer and the rare earth-richrare earth-transition metal amorphous alloy layer are appropriatelyselected so that recorded information can be magnetically reproduced,their coercive forces do not substantially change in the temperaturerange from room temperature to approximately 65° C. and the alloy layershave a tBr of 55 Gauss μm or more. Specific combinations of thetransition metal-rich rare earth-transition metal amorphous alloy layersand the rare earth-rich rare earth-transition metal amorphous alloylayers are, for example:

in the case of Tb_(x)Co_(1−x),

the combination of 14≦X≦22 and 25≦X≦35 (a units of mol %; the same isapplied the following);

in the case of Tb_(x)Fe_(1−x),

the combination of 14≦X≦23 and 25≦X≦34;

in the case of Tb_(x)(FeCr)_(1−x),

the combination of 15≦X≦24 and 26≦X≦36;

in the case of Tb_(x)(FeCo)_(1−x),

the combination of 14≦X≦23 and 25≦X≦34;

in the case of Dy_(x)(FeCo)_(1−x),

the combination of 16≦X≦22 and 24≦X≦33.

The thicknesses of the transition metal-rich rare earth-transition metalamorphous alloy layer and the rare earth-rich rare earth-transitionmetal amorphous alloy layer differ according to the kinds of alloylayers to be used, but preferably in the range of 5-45 nm.

The method of forming the alloy layers is not particularly limited, andany known method can be used. Among known methods, a sputtering methodis preferably used to form the alloy layers.

Incidentally, if the tBr is smaller than 50 Gauss μm, the SNR valuedecreases and it becomes difficult to record and reproduce information.A more preferable tBr is in the range of 57-135 Gauss μm.

The above-described two alloy layers are normally formed over the base.Either of the transition metal-rich rare earth-transition metalamorphous alloy layer and the rare earth-rich rare earth-transitionmetal amorphous alloy layer may be formed to face the base.

As in the case of the first information recording medium, it ispreferable that regular depressions and projections having apredetermined Ra or period are formed on the base. The kinds of baseswhich can be specifically used and the method of forming the regulardepressions and projections on the base are similar to those used forthe above-described first information recording medium.

As in the case of the first information recording medium, amagnetization inversion assisting layer may be provided between thesubstrate and the alloy layers, a substrate protecting layer may beprovided between the substrate and the alloy layers (if themagnetization inversion assisting layer is formed, between the assistinglayer and the substrate), and a surface protecting layer may be providedas the uppermost layer.

Similarly to the first information recording medium, the secondinformation recording medium of the present invention can be used as amagnetic recording medium, and also as a magneto-optical recordingmedium.

If either of the first and second information recording media of thepresent invention is used as the magnetic recording medium, a recordingand reproducing apparatus which records and reproduces information onand from the medium is not particularly limited, and any known apparatuscan be used. For example, an information reproducing apparatus has atleast a slider provided with a magnetic head. The magnetic head recordsand/or reproduces of information on and/or from the informationrecording medium. The magnetic head may be provided with separate headsfor recording and reproduction such as a recording head and a magneticreproducing head. If a thin-film coil for a magnetic disk, which iscapable of high-speed transfer magnetic field inversion, is employed inthe recording head, it is possible to realize high-density recordingwithout degrading the transfer rate of the recording head.

If either of the first and second information recording media of thepresent invention is used as the magneto-optical recording medium, arecording and reproducing apparatus which records and reproducesinformation on and from this medium has, for example, a slider providedwith a magnetic head and a light irradiating means. The lightirradiating means irradiates the information recording medium with lightto raise the temperature of the irradiated portion, thereby facilitatingrecording and reproduction of information. It also serves the role ofmaking recording marks far smaller. It is preferable to use lightemitted from a laser as the light for the irradiation, for example.

FIG. 2 shows one example of the construction of a recording andreproducing apparatus having the above-described light irradiatingmeans. Although the following description refers to the lightirradiating means as a laser light irradiating means, the presentinvention is not limited to laser light, and can use various kinds oflight. In FIG. 2, symbol A denotes an information recording medium, andreference numerals 4 and 6 denote a laser light irradiating means and amagnetic head part including a slider, respectively.

The laser light irradiating means 4 includes, if the laser light isused, a laser 41 which emits the laser light, a collimator lens 42 whichcollimates the laser light, a splitter 43 which transmits or reflectsthe laser light and, an objective lens 44 disposed in this order towardthe information recording medium A. Furthermore, on the reflection sideof the splitter 43, a half-wave plate 45 which rotates the plane ofpolarization of the laser light, and a polarizing beam splitter 46 whichseparates the laser light into a horizontal component and a verticalcomponent, are disposed in this order. Condenser lenses 47 and 49 whichcondense the output light of the horizontal component, and that of thevertical component, respectively, are disposed on the output side of thesplitter 43 and photodetectors 48 and 50 are disposed on the outputsides of the condenser lenses 47 and 49, respectively. An amplifier 51which calculates the difference between detection signals obtained fromthese photodetectors 48 and 50 and amplifies the obtained difference isconnected to the photodetectors 48 and 50. A signal output from theamplifier 51 is output to a switching terminal 65 of a switch part.

A magnetic head part 6 is provided with an amplifier circuit 62 whichreceives and amplifies an electrical signal corresponding to amagnetization direction detected by a slider 61 provided with a magnetichead, and an integrating circuit 63 which receives the amplified signaland shapes the waveform thereof. The signal from the integrating circuit63 is output to a switching terminal 66. Either of the signals output tothe switching terminals 65 and 66 is input to a demodulating circuit 64by switching a common terminal 67 of the switch part and demodulated tobe output signal.

According to the recording and reproducing apparatus shown in FIG. 2,the information recording medium A is irradiated with laser light fromthe laser light irradiating means 4 to heat the irradiated portion andbring the irradiated portion to a state in which information can beeasily recorded and/or reproduced. Thus, information can be recordedand/or reproduced on and/or from the heated region by the magnetic head.A schematic diagram illustrating this recording and/or reproduction ofinformation is shown in FIG. 3. In FIG. 3, reference numerals 11, 12 and13 denote the heated region, the magnetic head and a track pitch,respectively.

Specifically, by irradiating laser light during the recording, thecoercive force of the information recording film is made small, wherebya recording current can be made small. Further, it is possible to recordinformation on a medium which has a large coercive force at roomtemperature. On the other hand, by irradiating laser light during thereproduction, the value of magnetization of the information recordingfilm is made large, whereby the reproducing signal can be made large.

The present invention further provides an information recording andreproducing slider used for recording and/or reproducing information onand/or from the magneto-optical recording medium. The informationrecording and reproducing slider includes a laser light irradiatingmeans integrated with the slider, a recording head and a magneticreproducing head. The laser light irradiating means is positioned aheadof the recording head and the magnetic reproducing head in the directionof recording and reproduction of information.

The slider has the construction shown in FIG. 4 by way of example. InFIG. 4, reference numerals 21, 22 and 23 denote the slider, a slidersupporting means (for example, a spring) and a laser light irradiatingmeans (for example, an optical fiber), respectively. FIGS. 5 and 6 eachshow a cross-sectional view of a major part of the slider. In FIGS. 5and 6, reference numerals 31, 32 and 33 denote a recording head, amagnetic reproducing head and a laser light irradiating means,respectively. In FIGS. 5 and 6, the laser light irradiating means, therecording head and the magnetic reproducing head are integrated. Thelaser light irradiating means is positioned ahead of the recording headand the magnetic reproducing head in the direction of recording andreproduction of information (the direction of the arrow shown in thefigures). Since the irradiated laser light flows backward as the slidermoves forward and thus the temperature of the heated portion shows thesame distribution as the light, the information can be effectivelyrecorded and/or reproduced by arranging the recording head and themagnetic recording head behind the laser light irradiating means. Inaddition, since the laser light irradiating means, the recording headand the magnetic reproducing head are integrated, high-speed seek ispossible as compared with a related-art apparatus in which a laser lightirradiating means is separately disposed. The sliders shown in FIGS. 5and 6 differ in the arrangement of the recording head and themagnetically reproducing head.

In addition, a heat radiation layer may be provided on the bottom side(a side facing to the medium) of the slider in order to prevent therecording head and the magnetic reproducing head from being degraded bya rise in temperature caused by the laser light. The head radiationlayer preferably uses a material of good heat conductivity such asaluminum or copper.

The above-described recording and reproducing apparatus can be producedby forming, for example, an optical waveguide which includes LiNbO₃ as acore and a SiO₂ glass as a cladding formed on an AlTiC substrate as thelaser light irradiating means, and forming the recording head and themagnetic reproducing head on the optical waveguide by known means.

EXAMPLES

Specific examples of the present invention will be described below, butthe present invention is not at all restricted by any of the examples.

Example 1

A Ni₃P underlying layer having a thickness varied in the range of 0-1.5nm, a 2-nm-thick substrate protecting layer made of SiNx, a 50-nm-thickinformation recording film (magnetic film) made of Tb₁₅Fe₈₅ which is anamorphous alloy, a 3-nm-thick surface protecting layer made of SiNx, anda 3-nm-thick C (carbon) layer for improving the sliding characteristicsof recording and reproducing heads were laminated in this order over aglass substrate of Ra <0.05 nm (hereinafter referred to as a super flatsubstrate) by a sputtering process, thereby forming an informationrecording medium. Specifically, each of the layers was formed under thefollowing conditions:

magnetic film—sputtering gas: Ar

sputtering gas pressure: 0.5 Pa

applied power: 1 KW

underlying layer—sputtering gas: Ar

sputtering gas pressure: 2 Pa

applied power: 1 KW

substrate protecting layer and surface protecting layer—sputtering gaspressure: Ar and N₂

(gas mixture ratio: Ar/N₂=7/3)

sputtering gas: 0.3 Pa

applied power: 0.8 KW

C layer—sputtering gas: Ar

sputtering gas pressure: 0.5 Pa

applied power: 0.9 KW

The magnetic film of the obtained information recording medium exhibitedperpendicular magnetization and a coercive force of about 1 kOe.

Information of 200 kfci (equivalent to a mark length of 0.127 μm) wasrecorded on this information recording medium under the followingconditions and SNR at this time was measured:

rotating speed: 4,500 rpm

magnetic head: write width—2.0 μm

reproduction width—1.5 μm

reproduction—MR head

floating distance—30 nm.

In addition, under the same conditions, information of 70 kfci(equivalent to a mark length of 0.36 μm) was recorded on the informationrecording medium, and then information of 400 kfci (equivalent to a marklength of 0.064 μm) was overwritten to measure the characteristic (O/Wcharacteristic) of unerased components of frequency equivalent to theinformation of 70 kfci. In addition, the Ra of the underlying layer wasmeasured. The results are shown below.

thickness of 0, 8, 10, 20, 30, 40, 50, 60, 75, 80 underlying layer (nm)Ra (nm) 0.05, 0.10, 0.15, 0.23, 0.05, 0.73, 0.90, 1.20, 1.50, 1.70 SNR(dB) 11.5, 14.2, 15.8, 18.9, 21.2, 22.0, 22.2, 18.9, 16.2, 12.8 O/W (dB)−10, −26, −38, −42, −42, −43, −43, −42, −35, −12

In the case where no underlying layer was formed, a mark of accurate 1μm was not able to be recorded on the magnetic film although a magneticfield of about 3 kOe was applied by supplying a current of 60 mA to themagnetic head. This is considered to be due to the fact that since theexchange coupling force in the magnetic material is large and thedirection of magnetization easily assumes one direction. It was foundout, therefore, that when Ra was small, it was difficult to accuratelyform a mark on the magnetic film by the magnetic head. Contrarily, whenthe Ra of the underlying layer was made large, it was possible toimprove the SNR and the O/W characteristic. In particular, when therange of Ra was 0.1-1.5 nm, improvements in SNR and O/W characteristicwere remarkable.

The reason for the improvements in SNR and O/W characteristic seems tobe that in a system which magnetically reproduces information recordedon a magnetic film made of a rare earth-transition metal amorphousalloy, the exchange coupling force in the magnetic material lowers to anextent that information can be accurately recorded/reproduced ifadequate depressions and projections are formed on a base which formsthe magnetic film.

Example 2

Although in Example 1 the SNR and the O/W characteristic relative to theRa of the underlying layer were examined, in Example 2, the SNR and theO/W characteristic were examined on a medium in which regulardepressions and projections were directly formed on a glass substrate.

Information recording media were formed in a manner similar to that usedin Example 1, except that the super flat substrate used in Example 1 wasdipped in hydrochloric acid and then subjected to mechanochemicalpolishing to form various patterns of Ra values on the substrate. In amanner similar to that used in Example 1, the SNR and the O/Wcharacteristic relative to Ra were measured. The results are shownbelow.

Ra (nm) 0.05, 0.15, 0.23, 0.55, 0.73, 0.90

SNR (dB) 11.5, 15.4, 17.9, 21.7, 22.5, 22.1

O/W (dB) −10, −23, −39, −41, −43, −42

The above results show that it was possible to obtain results similar tothose of Example 1 by forming the regular depressions and projections onthe substrate.

Example 3

At present, crystalline magnetic bodies made of CoCrPtTa (for example,Co₇₇Cr₁₅Pt₆Ta₂) are widely used as magnetic films in magnetic recordingmedia. In this composition, Cr is used for promoting isolation ofmagnetic particles (physical separation of magnetic crystal grains).

An attempt at the addition of Cr to a rare earth-transition metalamorphous alloy film has been made in order to improve the chemicalstability of the magnetic film. In this case, since Cr is uniformlydispersed in the magnetic material of the rare earth-transition metal,and the film structure is amorphous, it has been generally consideredthat Cr does not have an action as shown in the above crystallinemagnetic recording medium. In Example 3, examination was made ofrecording and reproducing characteristics obtained in the case where Crwas added to TbFe formed on a underlying layer on which adequatedepressions and projections were formed.

Specifically, information recording media were formed in a mannersimilar to that used in Example 1 except that (Tb₁₅Fe₈₅)_(100−x)Cr_(x)was used for the magnetic film and a NiP layer of 30-nm-thick (Ra: 0.55)was used for the underlying layer, and variations in SNR with respect tox were measured. SNR was measured in a manner similar to that used inExample 1. The results are shown below.

Cr content (atom %) 0, 3, 7, 9, 12

SNR (dB) 21.2, 22.0, 22.5, 23.1, 23.2

From the above results, it has been found out that SNR can be improvedto a further extent by adding a nonmagnetic element such as Cr to anamorphous alloy.

Example 4

In the above-described examples, examinations were made into the rareearth-transition metal amorphous alloys which included TbFe as theirmajor constituents, whereas in Example 4, an examination was made into adifferent alloy.

Specifically, information recording media were formed in a mannersimilar to that used in Example 3, except that Tb₁₅Fe_(85−x)Co_(x) wasused for the magnetic film, and variations in SNR with respect to x weremeasured. SNR was measured in a manner similar to that used inExample 1. The results are shown below.

Co content (atom %) 0, 10, 20, 30, 35

SNR (dB) 21.2, 22.0, 23.0, 24.2, 24.5

From the above results, it has been found out that SNR can be improvedto a further extent by adding Co to an amorphous alloy. This isconsidered to be due to the fact that as the value of saturationmagnetization of the magnetic film increases, the level of a reproducingsignal increases.

Example 5

An examination was made into another different alloy film of RE-richDyFeCo which. DyFeCo is smaller in perpendicular magnetic anisotropy butlager in saturation magnetization value than TbFe, and accordingly thereis a possibility that DyFeCo can provide a far larger signal.Furthermore, the RE-rich DyFeCo is considered to be resistive to atemperature rise because the coercive force increases even if ambienttemperature rises.

Specifically, an information recording medium was formed in a mannersimilar to that used in Example 3, except that RE-rich Dy₂₅Fe₄₅Co₃₀ wasused for the magnetic film. The coercive force of this magnetic film wasabout 2 kOe and the compensation temperature at which the coercive forcereached infinity was about 130° C. SNR at 200 kfci was 24.5 dB. Thisresult was approximately the same as that of Tb₁₅Fe₅₅Co₃₀ of Example 4.

Then, variations in SNR of Dy₂₅Fe₄₅Co₃₀ and Tb₁₅Fe₅₅Co₃₀ with respect toa temperature rise were measured. Specifically, information was recordedin a manner similar to that used in Example 1, and measurement wasperformed on the SNR of the information recording medium after heatingthe information recording medium to a predetermined temperature and thencooling to a room temperature. The results are shown below.

heating temperature (° C.) 20, 40, 50, 60, 70, 80 Tb₁₅Fe₅₅Co₃₀ 24.2,24.2, 24.0, 23.5, 23.2, 22.9 Dy₂₅Fe₄₅Co₃₀ 24.5, 24.5, 24.4, 24.4, 24.4,24.4

From the above results, it has been found out that RE-rich magnetic filmis very effective against the temperature rise.

Example 6

In Example 6, examination was made of recording and reproducingcharacteristics obtained in the case where magnetic films havingdifferent magnetic characteristics were exchange-coupled to each other.

Specifically, an information recording medium was formed in a mannersimilar to that used in Example 3, except that used was a magnetic filmmade of a laminated body of a 15-nm-thick TbFe layer and a 35-nm-thickTbFeCo layer were laminated in this order from the underlying layer. Thecomposition of TbFe was determined to Tb₂₂Fe₇₈ so as to have anapproximate compensation composition, small magnetization and largecoercive force, whereas that of TbFeCo was determined to Tb₁₂Fe₅₀Co₃₈ soas to have small coercive force and a large saturation magnetizationvalue. (The former layer mainly serves the role of a recording layer,and the latter layer the role of a reproducing layer.)

The SNR of the obtained information recording medium was measured in amanner similar to that used in Example 1. The SNR was 24.6 dB which wasbetter than that of the TbFeCo single-layer film of Example 4.

Further, an information recording medium was formed in a manner similarto the above-described manner, except that a laminated body in whichTb₂₄Fe₇₆ and Dy₂₂Fe₄₅Co₃₃ were laminated in this order from theunderlying layer was exchange-coupled. The SNR of this informationrecording medium was 25.1 dB which was better than that of theDy₂₅Fe₄₅Co₃₀ single-layer film of Example 5, similarly to the case ofthe above-described laminated body of TbFe and TbFeCo.

From the above results, it has been found that even in the magneticrecording medium, it is possible to obtain SNR characteristicsunobtainable with the single-layer film, by exchange-coupling rareearth-transition metal amorphous alloys.

Example 7

In Example 7, examination was made of recording and reproducingcharacteristics obtained in the case where a perpendicular magnetizationfilm and an in-plane magnetization film were exchange-coupled to eachother.

Specifically, an information recording medium was formed in a mannersimilar to that used in Example 3, except that a laminated body in whicha 15-nm-thick GdFeCo layer (in-plane magnetization film) and a35-nm-thick DyFeCo layer (perpendicular magnetization film) werelaminated in this order from the underlying layer was exchange-coupled.Gd₃₅Fe₅₀Co₁₅ was used as the GdFeCo film, which was RE-rich andsaturated in magnetization at about 3 kOe and had almost no coerciveforce when a magnetic field was applied in the direction perpendicularto the surface of the GdFeCo film. In addition, Dy₂₅Fe₄₅Co₃₀ was used asthe DyFeCo film.

When information of 200 kfci was recorded on the obtained informationrecording medium with a recording current of 30 mA, a sufficiently highSNR of 25.5 dB was obtained.

On the other hand, in the case of an information recording medium formedin a manner similar to the above-described manner, except that noin-plane magnetization film was formed (i.e., the magnetic film was madeof only DyFeCo), the recording current required to obtain an SNR valueof approximately 25 dB in order to record information of 200 kfci was 50mA.

From the above results, it has been found that by incorporating thein-plane magnetization film as a magnetization inversion assistinglayer, magnetization inversion is assisted and recording magnetic fieldsensitivity can be improved.

Example 8

An information recording medium in which the constructions of Examples 6and 7 were combined, i.e., a magnetic film including a layer havinglarge coercive force and small saturation magnetization, a layer havingsmall coercive force and large saturation magnetization, and amagnetization inversion assisting layer (reproducing layer/recordinglayer/magnetization inversion assisting layer), was fabricated.

Specifically, an information recording medium was formed in a mannersimilar to that used in Example 3, except that a laminated body in whicha 10-nm-thick Gd₃₅Fe₅₀Co₁₅ layer, a 10-nm-thick Tb₂₄Fe₇₆ layer and a35-nm-thick Dy₂₂Fe₄₅Co₃₃ layer were laminated in this order from theunderlying layer, was used as the magnetic film.

From this information recording medium, it was possible to obtain an SNRvalue of 25.7 dB with respect to a signal of 200 kfci with a current of30 mA. From this result, it has been found that the construction ofreproducing layer/recording layer/magnetization inversion assistinglayer improves the SNR to a further extent.

Example 9

Although the above-described magnetic films were formed under the sameconditions, the size (i.e., Ra) of the regular depressions andprojections of their underlying layers may slightly vary according tothe sputtering conditions of the magnetic films. In Example 9,information recording media were formed by changing the sputtering gaspressure among the conditions for forming the magnetic film.

Specifically, information recording media were formed in a mannersimilar to that used in Example 1, except that the sputtering gaspressure was made 1.0 Pa. The SNRs of the obtained information recordingmedia were measured in a manner similar to that used in Example 1. Theresults are shown below together with the results in Example 1.

thickness of 0, 10, 20, 30, 40, 50 of underlying layer (nm) SNR (dB)11.5, 15.8, 18.9, 21.2, 22.0, 22.2 (for 0.5 Pa) SNR (dB) 11.5, 17.5,19.2, 22.2, 23.0, 23.2 (for 1.0 Pa)

It has been found that the film structure in the magnetic film inducedby the regular depressions and projections of the underlying layer isvery important in improving SNR, although recording characteristics arenot directly determined with respect to the Ra of the underlying layerof a magnetic film.

Example 10

In Example 10, SNR relative to the irregularity period of the underlyinglayer was examined.

Specifically, information recording media were formed in a mannersimilar to that used in Example 1, except that the periods of theirregular depressions and projections were varied while the Ra values ofthe regular depressions and projections kept nearly constant, bychanging applied power during the formation of their underlying layers(NiP layers). The SNRs of the obtained information recording media weremeasured in a manner similar to that used in Example 1. The results areshown below.

applied power (KW): 0.4, 0.7, 1, 1.4, 2.1, 2.9

irregularity period (nm): 6, 10, 20, 30, 40, 50

SNR (dB): 12.0, 16.3, 18.9, 19.2, 17.5, 12.4

From the above results, it has been found that the period of a columnstructure of a magnetic film formed on a underlying layer increases ordecreases by increasing or decreasing the period of the regulardepressions and projections of the underlying layer, and a period of10-40 nm is suited to the recording of information.

Example 11

Although reproduction was performed at room temperature in Examples 1 to10, the magnetization of a magnetic film may possibly increase byraising temperature. In particular, in the case of the rareearth-transition metal amorphous alloys, it is possible to skillfullychange magnetic characteristics with respect to temperature.

In Example 11, a temperature variation was applied to the magnetic filmof exchange coupled Tb₂₄Fe₇₆ and Dy₂₂Fe₄₅Co₃₃ used in Example 7 toincrease the magnetization of Tb₂₄Fe₇₆, whereby reproduction with alarge reproducing signal was performed.

In this example, the recording and reproducing apparatus shown in FIG. 2was used. In the apparatus shown in FIG. 2, laser light irradiated indiameter of about 15 μm, which was hardly narrowed, was used as meansfor raising temperature during reproduction. Temperature in a regionirradiated with the laser light was entirely raised.

By varying the power of the laser light, the following variations in SNRwere observed with respect to the variation in power. The followingresults are values obtained when information of 200 kfci was recorded.

irradiation power (mW) 0, 5, 10, 15, 20

SNR (dB) 25.1, 25.5, 26.1, 26.6, 25.5

From the above results, it has been found that SNR can be improved to afurther extent by heating the magnetic film. Incidentally, the reasonwhy SNR lowers at 20 mW is that a recorded signal starts to be erased.

Example 12

Although Example 11 used the recording and reproducing apparatus inwhich the recording and reproducing heads and the laser lightirradiating means are separately constructed, Example 12 used arecording and reproducing apparatus provided with a recording head, areproducing head and a laser light irradiating means that wereintegrated. More specifically, the laser light irradiating meansincludes a laser light generating device and an optical waveguide, andis positioned ahead of the recording head and the reproducing head inthe recording and reproducing direction. In this recording andreproducing apparatus, a positional relationship among a laser lightemitting point. The recording head and the reproducing head do not varyrelatively.

The above-described recording and reproducing apparatus and theinformation recording medium of Example 11 were used to performreproduction of information.

irradiation power (mW) 0, 2, 4, 7, 10

SNR (dB) 25.1, 25.5, 26.1, 26.6, 25.5

SNRs nearly equal to those of Example 11 were obtained, but in Example12, the irradiation power was able to be relatively lowered since thelaser light was narrowed. The diameter of the laser light was 0.5 μm.

Example 13

First, two kinds of information recording media were prepared by forminga 20-nm-thick SiN film, a magnetic film made of Tb₁₆Fe₈₄ (TM-rich) or amagnetic film made of Tb₂₈Fe₇₂(RE-rich), and a 20-nm-thick SiN film overa substrate in this order, and the magnetic characteristics of therespective information recording media were examined.

The magnetic film was formed using targets having each composition and aknown magnetron sputtering apparatus under the conditions of sputteringgas (Ar) pressure: 0.5 Pa and sputtering rate: 30 nm/m.

In the case of the magnetic film made of Tb₁₆Fe₈₄, the coercive force atroom temperature was 3 kOe, the coercive force at 65° C. was 2 kOe, andthe saturation magnetization was 200 emu/cc. In the case of the magneticfilm made of Tb₂₈Fe₇₂, the coercive force at room temperature was 3 kOe,the coercive force at 65° C. was 4 kOe, and the saturationmagnetization-was 150 emu/cc.

Then, as shown in FIG. 8, the above-described two kinds of magneticfilms were continuously laminated. Specifically, a 20-nm-thick SiN film,a 10-nm-thick NiP film and a 2-nm-thick C film were formed over asubstrate 1 in this order, thereby forming a underlying layer 2.Further, a 12-nm-thick magnetic film 7 made of Tb₂₈Fe₇₂ and a32-nm-thick magnetic film 8 made of Tb₁₆Fe₈₄ were continuously formedover the C film. After that, a 7-nm-thick protective layer 9 made of SiNand a 3-nm-thick solid lubricating layer made of C (not shown) wereformed in this order, whereby an information recording medium bothmagnetic films were exchange-coupled was obtained.

The obtained information recording medium exhibited a coercive force ofabout 2.7 kOe and a tBr of 58 Gauss μm at room temperature, and acoercive force of 4 kOe and a tBr of 60 Gauss μm at 65° C.

The above information recording medium was evaluated through recordingand reproduction performed with an actual magnetic disk drive in thefollowing manner.

The magnetic disk drive was disposed in a thermo-hygrostat maintained atabout 25° C. and recording and reproduction were performed through amerge type GMR head. When a recording current Iw was made about 15 mA;the signal amplitude was saturated, and the O/W characteristic (240 kfciwas recorded on 20 kfci) exhibited a good value of −40 dB. SNR at 240kfci exhibited a value of 21 dB.

In addition, the thermo-hygrostat was maintained at about 65° C. andrecording and reproduction were performed through the same merge typeGMR head. When the recording current lw was made about 17 mA, the signalamplitude was saturated, and the O/W characteristic exhibited a goodvalue of −38 dB. SNR at 240 kfci exhibited a value of 21.3 dB.

The signals recorded at room temperature and at 65° C., did not vary atall even after two hours, and SNRs obtained immediately after recordingwere retained.

Example 14

A TbFeCo film was used as a TM-rich film, and a DyFeCo film was used asan RE-rich film. Specifically, an information recording medium wasobtained in a manner similar to that used in Example 13, except that aTb₁₅Fe₇₅Co₁₀ film (Hc=2.7 kOe, Ms=200 emu/cc, film thickness=40 nm) anda Dy₂₉Fec),Co₁₀ film (Hc=2.5 kOe, Ms=130 emu/cc, film thickness=10 nm)were employed. The information recording medium exhibited a coerciveforce of about 3.1 kOe and a tBr of 84 Gauss μm at room temperature, anda coercive force of 3.2 kOe at 40° C. and a coercive force of 4 kOe at65° C.

Accordingly, at both of room temperature and 65° C., a magnetic field ofapproximately 3.4 kOe sufficed to magnetically record information onthis medium, and the recorded information did not disappear.

Moreover, the recording characteristics of the information recordingmedium and the stability of recorded data were examined with a magneticdisk drive similar to that used in Example 13, and the O/Wcharacteristic was a good value of −38 dB and an SNR of 22 dB wasobtained at 240 kfci. In addition, when two hours passed afterrecording, the SNR was 22 dB and the signal did not deteriorate.

Example 15

An information recording medium was obtained in a manner similar to thatused in Example 13, except that a Dy₂₀Fe₅₀Co₃₀ film (of thickness 20 nm)was employed as a TM rich film and a Tb₂₈Fe₆₀Co₁₂ film (of thickness 40nm) was employed as an RE rich film. The information recording mediumexhibited a coercive force of about 2.7 kOe and a tBr of 72 Gauss μm atroom temperature. The coercive force at 40° C. was 2.9 kOe, and thecoercive force at 65° C. was 3.1 kOe.

In addition, when two hours passed after recording, the SNR was 20.8 dBand the signal merely deteriorated to a slight extent.

Example 16

Information recording media were formed in a manner similar to that usedin Example 13, except that the periods of the regular depressions andprojections of NiP films constituting their underlying layers werechanged in the following manner. The periods of the regular depressionsand projections were adjusted by changing applied sputtering power. ThetBrs of the magnetic films were 58 Gauss μm, similarly to that inExample 13. The SNRs of the obtained information recording media at 240kfci were measured. The results are shown below.

applied power (KW): 0.4, 0.7, 1.0, 1.4, 2.1, 2.9

irregularity period (nm): 6, 10, 20, 30, 40, 50

SNR (dB): 15.0, 19.4, 21.0, 21.3, 21.2, 15.4

From the above results, it has been found that a more preferable SNR canbe obtained when the period of regular depressions and projections isapproximately 10-40 nm.

Example 17

Information recording media were formed in a manner similar to that usedin Example 13, except that the Ra values of the regular depressions andprojections of NiP films constituting their underlying layers werechanged in the following manner. Ra of the regular depressions andprojections were adjusted by changing the NiP films. The tBrs of themagnetic films were 58 Gauss μm, similarly to that in Example 13. TheSNRs and O/W characteristics at 240 kfci of the obtained informationrecording media were measured. The results are shown below.

thickness of 0, 8, 10, 20, 30, 40, 50, 60, 70, 80 NiP film (nm): Ra(nm): 0.05, 0.10, 0.15, 0.23, 0.55, 0.73, 0.90, 1.20, 1.50, 1.70 SNR(dB): 14.5, 19.2, 21.0, 21.3, 21.2, 22.0, 21.5, 19.0, 18.3, 12.8 O/W(dB): −10, −32, −40, −41, −41, −40, −43, −42, −35, −12

From the above results, it has been found that a more preferable SNR canbe obtained when Ra is approximately 0.1-1.5 nm.

Example 18

Information recording media were formed in a manner similar to that usedin Example 14, except that the thickness of the TbFeCo film and that ofthe DyFeCo film were changed in the following manner. The SNRs and tBrsof the obtained information recording media were measured. The resultsare shown below.

TbFeCo (nm): 90, 80, 60, 50, 40, 30, 29, 27, 25, 20, 20, 20 DyFeCo (nm):10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 25, 27 tBr (Gauss μm): 210, 184,134, 109, 59, 57, 56, 52, 46, 33, 27, 6 SNR (dB): 19, 21, 22, 23, 22,22, 21, 16, 14, 10, 5, 1

From the above results, it has been found that a preferable SNR can beobtained if tBr is 55 Gauss μm or more,. Moreover, it has been found outthat the range of 57-134 Gauss μm is more preferable.

The information recording medium according to the present invention canrecord information at an ultra high density while stabilizing very smallrecording marks and reproduce the recorded information with an existingmagnetic reproducing.

What is claimed is:
 1. An information recording medium comprising anunderlying layer formed on a substrate and an information recording filmformed on the underlying layer, the underlying layer having an Ra of 0.1to 1.5 nm, wherein the Ra of the underlying layer is larger than the Raof the substrate, and the information recording film containing as amajor component a rare earth-transition metal amorphous alloy capable ofmagnetically reproducing a recorded information.
 2. An informationrecording medium comprising an underlying layer formed on a substrateand an information recording film formed on the underlying layer, theunderlying layer having a period of 10 to 40 nm, and an Ra larger thanthe Ra of the substrate and, the information recording medium containingas a major component a rare earth-transition metal amorphous alloycapable of magnetically reproducing a recorded information.
 3. A sliderfor recording and reproducing information used for recording orreproducing on or from an information recording medium including anunderlying layer formed on a substrate and an information recording filmformed on the underlying layer, the underlying layer having an Ra of 0.1to 1.5 nm, wherein the Ra of the underlying layer is larger than the Raof the substrate, and the information recording film containing as amajor component a rare earth-transition metal amorphous alloy capable ofmagnetically reproducing a recorded information, the slider comprising alight irradiating means, a recording head and a magnetic reproducinghead that are integrated, the light irradiating means being locatedahead of the recording head and the magnetic reproducing head in thedirection of information recording and reproducing.
 4. A slider forrecording and reproducing information used for recording or reproducingon or from an information recording medium including an underlying layerformed on a substrate and an information recording film formed on theunderlying layer, the underlying layer having a period of 10 to 40 nm,and an Ra larger than the Ra of the substrate and, the informationrecording medium containing as a major component a rare earth-transitionmetal amorphous alloy capable of magnetically reproducing a recordedinformation, the slider comprising a light irradiating means, arecording head and a magnetic reproducing head that are integrated, thelight irradiating means being located ahead of the recording head andthe magnetic reproducing head in the direction of information recordingand reproducing.
 5. The information recording medium according to claim1, wherein information is recorded on and reproduced from theinformation recording film using a slider for recording and reproducinginformation.
 6. The information recording medium according to claim 2,wherein information is recorded on and reproduced from the informationrecording film using a slider for recording and reproducing information.7. The information recording medium according to claim 1, wherein the Raof the substrate is less than 0.05 nm.
 8. The information recordingmedium according to claim 2, wherein the Ra of the substrate is lessthan 0.05 nm.
 9. The information recording medium according to claim 1,wherein the underlying layer is made from a material selected from thegroup consisting of Ni, NiB, CrMo, Cr and Ti.
 10. The informationrecording medium according to claim 2, wherein the underlying layer ismade from a material selected from the group consisting of Ni, NiB,CrMo, Cr and Ti.
 11. The information recording medium according to claim1, wherein the Ra of the underlying layer is between 0.2 nm and 1.2 nm.12. The information recording medium according to claim 2 wherein the Raof the underlying layer is between 0.2 nm and 1.2 nm.
 13. Theinformation recording medium according to claim 2, wherein the period ofthe underlying layer is between 15 nm and 25 nm.